The mitochondrial DNA of lager brewing strains.
Sandra Rainieri, Yukiko Kodama, Yoshihiro Nakao, Wataru Miki
Institute for Advanced Technol, Suntory Research Center, 1 1 1 Wakayamadai, Osaka, 618 8503, Japan
Lager brewing strains are among the most important natural Saccharomyces hybrids for the fermentation industry; they originate from the mating of a S. cerevisiae and at least one non- S. cerevisiae parental strain, closely related to S. bayanus. We used RFLP and sequencing to investigate the nature and the inheritance of the mtDNA of 21 lager brewing strains. We then made a comparison with the mtDNA of several S. bayanus and S. uvarum strains and with a number of S. cerevisiae isolates (including some ale strains). In artificial Saccharomyces hybrids mtDNA is inherited randomly by only one of the parental strains. We tested both coding regions and intergenic sequences of mtDNA and our results show that the mtDNA of all the lager strains examined does not contain either coding or intergenic regions from S. cerevisiae. Sequencing of the COXII gene showed that lager strains and S. bayanus COXII are identical. However the RFLP patterns of lager strains obtained with three different restriction enzymes that can highlight the polymorphism of the intergenic regions, resulted different from S. bayanus patterns. These results can lead to two hypothesis; i) the inheritance of mtDNA in natural hybrids occurs in a different way compared to artificial hybrids ii) the industrial selection carried out on lager brewing strains, favoring those bearing optimal fermentation characteristics, has gradually lead to the extinction of strains naturally containing S. cerevisiae type mtDNA.